CANBERRA, Australia – Signaling a determination to counter a rising China, President Barack Obama vowed Thursday to expand U.S. influence in the Asia-Pacific region and “project power and deter threats to peace” in that part of the world even as he reduces defense spending and winds down two wars.

“The United States is a Pacific power, and we are here to stay,” he declared in a speech to the Australian Parliament, sending an unmistakable message to Beijing.

Obama’s bullish speech came several hours after announcing he would send military aircraft and up to 2,500 Marines to northern Australia for a training hub to help allies and protect American interests across Asia.

He declared the U.S. is not afraid of China, by far the biggest and most powerful country in the region.

China immediately questioned the U.S. move and said it deserved further scrutiny.

Emphasizing that a U.S. presence in the Asia-Pacific region is a top priority of his administration, Obama stressed that any reductions in U.S. defense spending will not come at the expense of that goal.

“Let there be no doubt: in the Asia-Pacific in the 21st century, the United States of America is all in,” he said.

For Obama, Asia represents both a security challenge and an economic opportunity. Speaking in broad geopolitical terms, the president asserted: “With most of the world’s nuclear powers and some half of humanity, Asia will largely define whether the century ahead will be marked by conflict or cooperation, needless suffering or human progress.”

Virtually everything Obama is doing on his nine-day trip across the Asia-Pacific region has a Chinese subtext, underscoring a relationship that is at once cooperative and marked by tensions over currency, human rights and military might.

China’s military spending has increased threefold since the 1990s to about $160 billion last year, and its military recently tested a new stealth jet fighter and launched its first aircraft carrier. A congressional advisory panel on Wednesday urged the White House and Congress to look more closely at China’s military expansion and pressed for a tougher stance against what it called anticompetitive Chinese trade policies.

The expanded basing agreement with Australia is one of several initiatives Obama has taken likely to set Beijing on edge at a tricky time. The U.S. is China’s second largest trading partner, and the economies are deeply intertwined. Chinese leaders don’t want the economy disrupted when global growth is shaky and they are preparing to transfer power to a new leadership next year.

Responding to questions at a news conference Wednesday with Australian Prime Minister Julia Gillard, Obama sought to downplay tension between the world powers. “The notion that we fear China is mistaken,” he said.

Obama avoided a confrontational tone with China in his speech to the Australian parliament, praising Beijing as a partner in reducing tensions on the Korean Peninsula.